This research includes five interrelated projects representing an integrated approach to questions of basic and clinical significance for the development and optimal application of cochlear prostheses. The program is a multi-disciplinary approach that cuts across a number of basic science disciplines including anatomy, audiology, human psychophysics, animal psychophysics, physiology, and engineering/biophysics and integrates these with clinical issues from Otolaryngology. Overall clinical goals of the program are to develop measures to assist in selection of candidates for implantation and that will guide implantation and rehabilitation strategies to optimize the benefits derived from the implant and to contribute to better cochlear prostheses. Basic goals include an improved understanding of the mechanisms underlying these measures and a description of prosthesis function at levels of the biophysics of the cochlea, encoding and processing in the CNS, structure of peripheral and central auditory structures, and perception. The projects include psychophysical studies of hearing in monkey and guinea pigs; biophysical studies of current flow and distribution in the inner ear; physiological studies of the encoding and processing of electrically evoked auditory activity; anatomical studies of the consequences of deafness on peripheral and central auditory structures and their reduction with electrical activation of the auditory pathways; and human psychophysical studies of the dependency of perception on spatial-temporal characteristics of stimulation. The results of these studies will be integrated with the human clinical implant research and service program ongoing in the Department of Otolaryngology's Cochlear Prosthesis Program (now the largest in the United States). This program of research can provide fundamental knowledge about the mechanisms of the auditory system that underlie benefits provided by the cochlear prosthesis as well as new insights into basic auditory system function.